Catalysts are materials that can change the rate of a chemical reaction without being consumed by the chemical reaction themselves. Catalysts may allow reactions to be carried out in moderate conditions (e.g., lower temperatures and pressures) by involving different transition states or lower activation energies. For example, noble metals (e.g., gold (Au), silver (Ag), platinum (Pt), and palladium (Pd)) are widely used in catalytic converters in vehicle exhaust systems.
The lack of choices of noble metals generally limits their performance as catalysts. In order to more efficiently and effectively use these noble metals as catalysts, different substrates have been tested to change the chemical potentials of the noble metals through charge transfer. Unfortunately, however, such chemical potential changes are generally on a scale too small to introduce a significant/drastic change in the catalytic behavior of the noble metals.